The genetically-diabetic mouse (C57B1/KsJ, db/db) was defective in many immunologic parameters for example, the mice were deficient in numbers of lymphocytes and peritoneal macrophages, in the response of lymphocytes to ConA, and in the capacity to phagocytose dead yeast cells. The capacity to elicit delayed footpad responses and to release lymphokines in vivo into the circulation were depressed. These mice were highly susceptible to intravenous infection with Candida albicans. The administration of an appropriate dose of alloxan produced a prolonged state of hyperglycemia, which persisted through 31 days. In 14 days after such treatment, a depression of many immunologic parameter occurred. Although most of these returned to normal after 14 days, the hyperglycemia and susceptibility to infection with C. albicans persisted.